In chemical and biological laboratories, it is often necessary to perform analytical and/or experimental assays or procedures on large numbers of laboratory specimens. For example, a lab technician might need to determine the reaction of many different specimens against one or more reagents, such as labeled probes. Common tasks that are performed for each sample include reagent transfers (e.g., aspiration and dispensing), mixing and stirring, as well as reading the results of each assay.
Typically, in years past, each sample was processed in its own, separate container, such as a tube or flask, in a largely manual fashion. Moreover, the early methods generally provided for the processing of only one or a few samples at a time and, thus, were time consuming and labor intensive. More recently, arrays of reaction wells (e.g., 96 wells arranged in an 8×12 array) formed in a tray or plate have become popular for separately performing numerous reactions at substantially the same time. Although parallel processing brought a substantial increase in throughput, many fundamental laboratory procedures continued to be carried out in a largely manual fashion In an effort to further increase throughput and decrease costs, many laboratory directors are now moving toward the use of automated instrumentation, and even higher-density plates, e.g., 384, 1536, or higher. The automation and parallel performance of common tasks has greatly streamlined the processing of samples, increasing lab efficiency and eliminating many sources of errors (e.g., technician errors).
Notwithstanding such benefits, the combination of high-density array formats and automated instrumentation has presented new problems that need to be addressed. One particularly vexing problem relates to the proper alignment of each reaction well of a multi-well plate on the support surface of a plate-handling machine. It should be appreciated that each well must be very accurately positioned in order for one or more acting members, e.g., pipette tips or optical sensors, to address and operate on them. For example, aligning each member of an array of pipette tips over an array of reaction wells can be a very challenging task. The difficulties of alignment tend to increase with the array size(s) involved.
Many conventional plate-handling machines locate multi-well plates by engaging the peripheral edge or sidewall of the plate against some fixed locating feature on the instrument, such as walls or bumpers disposed along two or more sides of a plate-support surface. Unfortunately, the position of each well in relation to the peripheral edges or sidewalls of many plates tends to vary markedly from plate to plate, even with plates of the same model from a single manufacturer. Such variations can arise from a variety of causes. For example, current manufacturing tolerances for a plate's peripheral features are typically not very rigorous, especially as compared to those for the wells themselves—which can be very exacting. Also, the relatively soft, deformable plastics from which most plates are formed, e.g., polyethylene or polypropylene, can introduce dimensional variations between plates. In situations where the automated machinery fails to accurately align the plates, manual intervention is often required, thus significantly reducing the effectiveness of the automation.
Clearly, there is a need for an improved apparatus and method for quickly and accurately aligning each well of a multi-well plate on the plate-support surface of a plate-handling machine.